1. Field of the Invention
The present invention relates to a method for preparing a hydrocarbon conversion catalyst. More particularly, this invention relates to the preparation of a substantially liquid phase hydrocarbon conversion catalyst without the use of an organic solvent.
2. Description of the Prior Art
The liquid phase strong acid catalyst comprising HF and TaF.sub.5 is known to be useful in promoting various hydrocarbon conversion reactions (see, for example, U.S. Pat. Nos. 2,683,763; 2,683,764; 3,728,411; 3,852,184; 3,888,937; 3,901,790; 3,948,761, as well as application Ser. No. 586,176, filed June 12, 1975, the disclosures of which are incorporated herein by reference). These reactions include isomerization, alkylation, disproportionation, naphthene cleavage, aromatic hydrogenation, and the like. It is also known that the effectiveness of this catalyst system for such hydrocarbon conversion reactions is related to the molar ratio of hydrogen fluoride to tantalum pentafluoride. More particularly, in order to maximize catalyst activity and activity maintenance, it is desirable to operate these processes at a catalyst composition wherein the molar ratio of HF to TaF.sub.5 is at least 1, preferably at least 5, more preferably at least 10 and most preferably within the range of from 5 to 40. However, at such ratios, TaF.sub.5 is not completely soluble in HF under the process conditions normally associated with said hydrocarbon conversion processes, such that the catalysts exists as a slurry. This creates operating problems related to homogeneous catalyst transfer, losses of TaF.sub.5 via deposition and line plugging. To alleviate this problem, the prior art has suggested the use of an organic solvent to solubilize the catalyst. A very effective solvent is benzene. However, substantial quantities of benzene, i.e. up to 50 mole percent on TaF.sub.5, are required. Such amounts of benzene depress catalyst activity and favor the formation of undesirable compounds that tend to adversely affect the ability of the catalyst to effect the hydrocarbon conversion reaction. In addition, about a 35 mole % on TaF.sub.5 of naphthenes, e.g. methylcyclopentane, have also been found to be suitable catalyst solubilizers. However, the resultant solution is sensitive to variations in process conditions such that TaF.sub.5 will precipitate if temperature and hydrogen partial pressure are not properly controlled. In addition, methylcyclopentane tends to react with components of the feedstock, particularly aromatics, to form catalyst poisons. Thus, it would be desirable to have available a simple and convenient method to solubilize the HF/TaF.sub.5 catalyst system without the disadvantages attendant in the prior art processes.